Recently, a route guidance apparatus for presenting a route guidance sentence and a simplified map to a destination for a pedestrian is developed. This route guidance apparatus is a simple portable device or is loaded to a portable communication terminal such as a cellular-phone or a personal data assistant (PDA).
A route guidance technique using the route guidance sentence and the simplified map is disclosed in the following two references.
(1) TECHNICAL REPORT OF IEICE, PRU95-215(1996-02), “Interactive Generation of a Route and Its Application to Generating a Sketch Map Drawing in a Map Image Information System” Masahiko HORIE, Toshihiro KIMURA, Noboru BABAGUCHI, Seiichiro DAN and Tadahiro KITAHASHI
(2) TECHNICAL REPORT OF IEICE, PRMU96-156(1997-01), “Modeling of Geographic Road Structure for Generation of Sketch Map Image and Linguistic Guide” Toshihiro KIMURA, Yoshihiro SUZUKI, Seiichiro DAN, Noboru BABAGUCHI and Tadahiro KITAHASHI
As for generation of the route guidance sentence, in reference (1), for example, a sentence “Please go forward to the west direction by 20 meters.” or “Please turn to the right at the junction.”, can be presented. However, especially, numerical value representing distance such as “** meters” is difficult for a pedestrian to apply. Furthermore, innumerable junctions exist in a town area, and the pedestrian often mistakes a junction indicated by the route guidance sentence for another junction. Accordingly, such route guidance sentence is not always easy for the pedestrian to sufficiently understand.
In reference (2), for example, a route guidance sentence such as “This road joins another road.” or “You advance to ** at a crossroads.”, is only presented. This route guidance sentence is more difficult for the pedestrian to understand than the route guidance sentence disclosed in the reference (1).
Furthermore, in the reference (2), generation of a simplified map for guidance using a signpost for pedestrian (i.e., a landmark) is disclosed. However, generation of a route guidance sentence using the landmark is not disclosed in the references (1) or (2). In the reference (2), the target object is reserved. As for other landmarks, the landmark far from a main junction is removed in order to simply present the landmark. However, if this method is used for generation of the route guidance sentence, for example, a complicated route guidance sentence using many landmarks is generated at a place neighboring the main junction. Thus, easiness of the route guidance produces a contrary effect.
As mentioned-above, in the known route guidance technique, presentation of the route guidance sentence is not always easy for the pedestrian to understand, and it often happens that the pedestrian misunderstands a junction point, a joint point, or a divergence point indicated by the route guidance sentence.
Furthermore, a method for effectively utilizing landmarks for generation of the route guidance sentence is not found. In short, it is impossible to execute easy route guidance for the pedestrian by using landmarks.